The president of MTV Networks abruptly left the music television broadcaster last night in the latest of a series of sudden departures unsettling the top ranks of the American media empire Viacom. Michael Wolf parted company with MTV after 15 months in the job. His exit came 24 hours after the president of Viacom's Hollywood studio, Paramount Pictures, resigned.

Mr Wolf, a former music industry consultant at McKinsey & Co, was recruited last year with a mandate to bolster the digital efforts of the group of channels, which includes MTV, VH1, Nickelodeon and Comedy Central. The gossip website Gawker.com broke news of Mr Wolf's move, claiming he had been ousted by Viacom's 83-year-old chairman, Sumner Redstone. Mr Wolf later told reporters he had not been forced to resign.

In September, Mr Redstone fired the group's chief executive, Tom Freston, in a move which prompted suggestions that the chairman, who owns 70% of Viacom's voting shares, was tightening his grip. Mr Freston received a payoff of $62m (£32m). He was replaced by Philippe Dauman, a close associate of Mr Redstone.

Before that, Mr Redstone had severed ties with Tom Cruise on the grounds that the actor's eccentric public behaviour was damaging box office receipts of movies such as Mission Impossible 2.

This week, Paramount Pictures' president, Gail Berman, regarded as one of Hollywood's most powerful figures, resigned less than two years into her job.